To assure product quality in the manufacture of integrated circuits it is desired to test each individual circuit. A common practice is to use test equipment which has a load board set up to test the specific type of circuit under test. A socket on the board for receiving the circuits under test is equipped with a plurality of contacts which are connected to the test circuit and which are moved by a solenoid actuator into contact with terminals on the IC package. The test equipment includes a handler which inserts each IC package into the socket for testing and removes it after the test.
In practice, cartridges or trays of IC packages of a given production lot are loaded into the test equipment and the packages are inserted one by one into the test station by the handler and a test is performed on each one to determine whether the packages meet specifications. To assure that the test circuit is performing properly the circuit is calibrated occasionally by manually inserting a pre-tested standard IC package of the same type as the lot being tested into the test station and running a test. This halts the normal production flow and production devices may be removed from the handler to prevent mixing with the standard device. If the device passes, the test system is confirmed as good and production flow resumes. If the device fails, interpretation of test results must be accomplished by qualified personnel. Finally, maintenance or calibration may be required. Checking the test system in this manner is done only after a problem is discovered or at scheduled calibration intervals. Typically, such a test is performed at the beginning and end of each production lot or at the start of the work day.
Shortcomings of this practice are:
1) A problem is not detected as it drifts into being. It is detected only after it has become serious. PA1 2) A separate manual cycle of intervention and device handling is required. PA1 3) Interpretation of test results is required. PA1 4) Usually an unknown number of devices are involved. This may allow marginal or bad parts to the released.